Loop of Henle: Vasa Recta

Role of the Vasa Recta (capillaries paralleling the loop of Henle)

1. Vasa recta vessels resemble other capillaries in their high permeability to sodium, chloride, urea, and water

2. Blood in the vasa recta capillaries entering the medulla loses water and gain NaCl and urea progressively as it descends

3. When blood flow in the vasa recta capillaries reverses direction and ascends from the medulla to the cortex, it progressively gains water and loses NaCl and urea

4. The blood leaving the vasa recta is approximately iso-osmotic with normal plasma, and it carries away from the medulla the reabsorbed NaCl and water. Thus, blood leaves the medulla at about the same osmolality that it entered by the mechanism of countercurrent exchange

5. This anatomical arrangement, combined with the relatively low blood flow to the medulla, permits sufficient perfusion for nutrition without destroying the high osmolality of the medulla

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